Hui Li  , Chengfei Liu  , Maria E Orlowska  , 
    Extended Algebra and Calculus for Object-Relational Database,
    Asian Journal of Information Technology,
    Volume 3,Issue 5,
    2004,
    Pages 386-399,
    ISSN 1682-3915,
    ajit.2004.386.399,
    (https://makhillpublications.co/view-article.php?doi=ajit.2004.386.399)
    Abstract: The converging trend of relational database technology and object-oriented technology results in ojbect-relational database systems, which opens up the type system of the traditional model to allow for the addition of new data types. Such as ADTs, references and collections. Traditional relational query languages need to be extended to handle the more complex structure, so do the query systems whcih form the underlyin gstructure of query languages. In this paper, we propose an object-relational data model which extends the relational model with add-on object features. We then define a tuple calculus and an algebra which are extended from their relational counterparts. They fully incorporate relational query operations, while supporting some new features to handle complex data. We also prove the equivalent expressibility between the extended tuple calculus and algebra.
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